The invention relates to an anti-counterfeit method that can protect confidential documents or sales articles against counterfeit. More particularly, the invention provides a method that can conceal the authentication mark of the article in such a manner that it is visible only with the use of a specific identification system.
Along with the technical progress in various fields such as mechanical processing, electro-forming, scanning techniques, or printing techniques, effective anti-counterfeit measures have to be continuously improved.
Presently, commonly used anti-counterfeit methods are based on the use of a transparent protecting film that covers laser holographic layers or laser anti-counterfeit structures of diffraction optical grating that are attached on the article to conceal an authentication pattern. Concealed by means of the laser holographic layers or laser anti-counterfeit structures of diffraction optical grating, the authentication pattern however can be displayed via light projection thereon. Moreover, a counterfeiter can remove the transparent protecting film easily and copy the authentication pattern concealed in the laser holographic layers or laser anti-counterfeit structures of diffraction optical grating by electro-forming. In addition, the counterfeiter can desirably produce a falsification to replace the authentic laser label, but common people are usually incapable of distinguishing this falsification without a comparison with the authentic label. Furthermore, as printing techniques and digital acquision techniques progress, accurate printing anti-counterfeit patterns can be also easily reproduced through high resolution scanning and printing to obtain a falsified version hardly discernable.
Another method known in the prior art is the use of two optical gratings or two holographic layers among which one is an authentication element. The authentication pattern becomes visible only once the authentication optical grating or holographic element is properly superposed over the other optical grating or holographic layer. Such a method thus favorably allows the user to easily authenticate an article. However, the fabrication of holographic elements or optical gratings is difficult to achieve and not economical.
It is therefore an object of the invention to provide an anti-counterfeit method that overcomes the above problems by concealing the authentication pattern in a manner not to be directly visible, and that is difficult to falsify.
To achieve the above and other objectives, the anti-counterfeit method of the invention conceals an authentication pattern in a retarder where the authentication pattern is incorporated in a concealed pattern region and a background region of different phase retardation. To authenticate the authentication pattern, the invention further provides an identification system in which the patterned retarder and one or more polarizers are to be assembled. The identification system polarizes the light that passes through the retarder and produces different transmittances of the concealed pattern region and background region, and thereby displays the authentication pattern. To improve protection against counterfeits, the invention further conceals the authentication pattern in a plurality of retarders that must be assembled with one another to display the authentication pattern. The retarder carrying a part of the authentication pattern with the polarizers can therefore assembled within the identification system to achieve a more effective anti-counterfeit measure.
To provide a further understanding of the invention, the following detailed description illustrates embodiments and examples of the invention, this detailed description being provided only for illustration of the invention.